A separate classification of rigid conduit (NEC Article 347) covers raceways
that are formed from such materials as fiber, asbestos-cement (not as serious
an environmental concern as it might sound), soapstone, rigid polyvinyl chloride
(PVC), and high density polyethylene.

FIGR. 17 Typical overhead conduit bank installation. Note that due to field
conditions the insert (a) for hanger rods was inadequate and an additional
insert (b) was added. This conduit bank uses EMT, which has a pipe-wall thickness
approximately one-third that of heavy-wall rigid conduit. The resulting weight
difference in a large bank such as this is very pronounced. EMT joints are
made with set screw fittings (c). Note how individual conduits are fixed by
clamps to the trapeze channel (d). (Courtesy of Republic Steel Corp.)

For use above ground, such conduit must be flame-retardant, tough, and resistant
to heat distortion, sunlight, and low-temperature effects. For use underground,
the last two requirements are waived. Generally, nonmetallic conduit may be
used without restriction in nonhazardous areas within the physical limitations
of the material involved. Thus, plastic conduit has a tempera ture limitation,
asbestos-cement has considerable physical strength limitations, and so on.
As a result of these limitations, PVC conduit is the material of choice for
indoor exposed use, and asbestos- cement, fiber, and PVC plastic for outdoor
and underground use. A separate ground wire must be provided because the ground
provided by a metallic conduit is absent.

22. SURFACE METAL RACEWAYS (METALLIC AND NONMETALLIC)

These raceways are covered in NEC Article 352.

Surface metal raceways and multi-outlet assemblies may be utilized only in
dry, nonhazardous, noncorrosive locations and may generally contain only wiring
operating below 300 V. Such raceways are normally installed exposed, in places
not subject to physical injury.

The principal applications of surface metal raceways are:

1. Where economy in construction weighs very heavily in favor of surface raceways
and where expansion is anticipated (FIGR. 19)

2. Where outlets are required at frequent intervals and where rewiring is
required or anticipated (FIGR. 20)

3. Where access to equipment in the raceways is required and/or where necessary
due to the nature of the wiring (FIGRs. 19, 21, 22, and 23)

4. Where the extensive and expensive cutting and patching required to "bury" a
raceway during rewiring is to be avoided (FIGR. 24)

FIGR. 18 This is a particularly good application of liquid tight, flexible
conduit because it provides weatherproofing and mechanical isolation of the
vibration-producing equipment. (Courtesy of Electri-Flex Company.)

FIGR. 19 Three-section nonmetallic baseboard-type raceway measures 4 in. H
and 1.5 in. D (100 × 38 mm). The three sections are intended for telephone,
power, and data cabling. The junction box on the right protrudes so as not
to lessen the raceway wiring space. It is equipped with vertical dividers to
keep the three types of wiring completely separated. The elevated wall box
on the left contains telephone and data cable outlets and connects only to
the low-voltage portions of the raceway. (Photo courtesy of Hubbell, Inc.)

FIGR. 20 Large-capacity surface metal raceways are particularly useful for
wiring in full-access floors (see Section 28) because of the heavy wiring
(see wall box) and frequent rewiring. The perforated floor tile in the foreground
is used to supply laminar airflow in this clean room at an integrated circuit
manufacturer's facility. (Photos courtesy of Walker Systems, A Wiremold Company.)

FIGR. 21 Multichannel nonmetallic surface raceway with snap-in connector modules
for data network, signal, and power wiring systems. (Similar metallic raceways
are also available.) The raceway itself measures 4½ in. H × 1 in. D (115 ×
25 mm). The internal dividers are movable or entirely removable, which permits
varying the number and size of the wiring channels. The principal application
of this type of wireway is in commercial occupancies using extensive desktop
data-processing and communication equipment. (Courtesy of Panduit.)

FIGR. 22 The frequent wiring changes required for theater and exhibition lighting
are easily made when the wiring is run in a suspended surface raceway. (Courtesy
of Walker Systems, A Wiremold Company.)

23. OUTLET AND DEVICE BOXES

These boxes are generally of galvanized stamped sheet metal. The most common
sizes are the 4-in. (100-mm) square and 4-in. (100-mm) octagonal boxes used
for fixtures, junctions, and devices and the 4 × 21 8 in. (100 × 54 mm) box
used for single devices where no splicing is required. Box depths vary from
1½ to 3 in. (38 to 76 mm). Nonmetallic boxes may be used with NM and NMC cable
and with nonmetallic conduit installations. In wet locations and for outdoor
work, cast-iron or cast aluminum boxes are recommended.

An NEC (Article 300-21) requirement that electrical penetrations in fire-rated
floors be de signed to maintain fire ratings has spurred electrical manufacturers
to produce a line of poke through fittings to meet this need. (This requirement
applies also to walls, ceilings, and partitions.) One such design is shown
in FIGR. 25. These electrical penetrations have become increasingly prevalent
in existing commercial spaces where the expanded need for desktop power and
data wiring can be met most economically and rapidly by through-the-floor feeds
from accessible wiring in the suspended ceiling plenum below. In addition,
these fittings facilitate the electrical wiring relocations so common in rental
office occupancies.

FIGR. 25 Typical poke-through electrical fitting mounts in a 4-in. (100-mm)
hole. It is wired from underneath with the required power, telephone, signal,
and data cables. Power and low-voltage cables are separated as required by
code. Units are available prewired or suitable for field wiring, and adaptable
for varying floor thicknesses. The floor fitting is provided with power, telephone,
and data cable outlets as required for the specific installation. (Courtesy
of Walker, Division of Wiremold.)

FIGR. 23 The basic raceway illustrated is 17 8 in. D × 3 3 16 in. W (48 ×
81 mm). It is shown with a divider installed, permitting use of the top section
for power wiring and the bottom section for low-voltage wiring. Because data
and communication cables are frequently supplied with factory-installed terminations
(as in the photo), a raceway where the cable can be laid in rather than pulled
in is required. Also, terminal strips and other equipment can be installed
in the low-voltage section of these large race ways, making the use of separate
terminal cabinets unnecessary. (Courtesy of Walker Systems, A Wiremold Company.)

24. FLOOR RACEWAYS

In commercial spaces with large open floor areas, it is common practice to
place desks and other work stations throughout the space, at considerable distances
from permanent walls containing electrical services. Because each workstation
in a modern office requires electric power for a computer, desk lamp, and other
common equipment plus a telephone line, a computer network connection, and
possibly a data outlet, the problem of bringing these services to the workstations
with a minimum of exposed wiring is critical. The required outlets can be installed
on the floor adjacent to or under the workstations or, if partial-height partitions
are used, within these partitions.

To bring the various electrical and communication services to the user, in
the absence of any sort of overall floor raceway system, the installing contractor
has one of four choices:

1. Channel the floor and install a conduit in the channel, connecting it to
the nearest wall out let. Patch the chased portion of the floor.

2. Install a surface floor raceway. The usefulness of this technique is very
limited because it presents a tripping hazard and problems with routine floor
cleaning.

3. Drill through the floor twice and connect the new outlet to a nearby existing
floor or wall outlet via a conduit on the underside of the floor slab. Floor
penetrations must be fireproof.

4. Drill through the floor and run a conduit in or on the ceiling below. When
using this technique, special poke-through fittings are avail able that restore
the fire rating of the slab (see FIGR. 25). These fittings are designed to
carry all the electric services normally required at a workstation. They can
then be connected to a single-location multiservice floor outlet group, as
in FIGR. 25, or used to wire the partitions in a workstation, as in FIGR. 26.

All four of these methods have serious disadvantages; method 1 is labor intensive,
method 2 is unsightly and presents a safety hazard, methods 3 and 4 disturb
the occupants below, and all four methods are generally inflexible and therefore
unsuitable for spaces where reasonable changes in wiring and workstation location
are anticipated. For these reasons, overall-access in-floor and underfloor
raceway systems were developed and are widely used in high-grade commercial
and institutional spaces.

The NEC recognizes three types of in-floor raceways:

Underfloor raceways-Article 354 Cellular metal floor raceways-Article 356
Cellular concrete floor raceways-Article 358 All three types are applicable
to all types of structures, and none may be used in corrosive or hazardous
areas. The fundamental difference between them is that underfloor raceways
are added on to the structure, whereas cellular floor raceways are part of
the structure itself-and therefore have a pronounced effect on architectural
coordination. (Underfloor duct systems antedate poke through fittings, which
are a relatively recent development.)

25. UNDERFLOOR DUCT

These raceways may be installed beneath or flush with the floor. They find
their widest application in office spaces because their use permits placement
of power, data, and signal outlets close to desks and other furniture, regardless
of spatial layout. Under floor duct systems were widely employed until the
introduction of what may be called over-the-ceiling ducts (in contrast to under-the-floor
ducts) and flat-cable under-carpet wiring. These systems are discussed in Section
29 and 30. The reason that alternative systems were developed is simply economic:
underfloor duct systems are expensive and, because they are inflexible, being
literally cast in concrete, they are frequently underutilized in one area while
being inadequate in another. Before discussing the relative merits of systems,
however, an understanding of what underfloor duct systems are and how they
are assembled and utilized is necessary.

An underfloor duct system is simply an arrangement of parallel rectangular
metal or heavy plastic raceways laid on the structural slab and covered with
concrete fill. Access to the wiring in these distribution ducts is via inserts
that connect to openings in the ducts and terminate in floor fit tings for
both power and signal/data wiring. Cable feeds to the distribution ducts are
supplied by a second set of rectangular raceways called feeder ducts, usually
laid at right angles to the distribution ducts.

In a single-level underfloor duct system, the distribution and feeder ducts
are on the same level,

and the interwiring between them is accomplished in junction boxes. The advantage
of a single-level system is shallow concrete fill, normally 2½ to 3 in. (64
to 76 mm). The limiting constraint of a single level system is the junction
box, which becomes more complex and multisectioned with an increasing number
of ducts and wires. Newer systems utilize a one-piece triple-cell duct for
both distribution and feeder ducts, with factory set inserts every 24 in. (610
mm) that straddle all three cells at once (FIGR. 27). By placing distribution
ducts on 5-ft (1.5-m) centers with adequate crosswise feeder ducts and utilizing
large flat junction boxes, a cost-effective installation adequate for all but
the heaviest wiring demands can be assembled.

FIGR. 26 Typical application of a poke-through fitting to provide power, telephone,
and data service to a modern workstation. This drawing shows the electrical
services being tapped at junction boxes in a hung ceiling conduit system on
the floor below. The ceiling wiring system can also be a raceway network in
lieu of the hard-wiring shown here. (From AIA: Ramsey/Sleeper, Architectural
Graphic Standards, 11th ed. 2007. Reprinted by permission of John Wiley & Sons.)

Because the initial cost of a full underfloor system is high, an alternative
arrangement utilizes only feeder ducts on approximately 25-ft (7.6-m) centers,
with flat (under-carpet) cable box connectors spaced approximately every 20
ft (6.1 m) along the feeder ducts. The low-tension (voltage) portion of this
system relies completely on flat telephone and data transmission cables, including
fiber-optic (FO) cables.

Because these cables are generally precut and factory terminated, the system
requirements must be care fully analyzed (see Section 29) before committing
to a complete under-carpet wiring system.

A two-level underfloor duct system is essentially the same as a single-level
system except that the distribution ducts and feeder ducts are on different
levels (FIGR. 28). This arrangement has the advantages of simplifying junction
boxes and of giving the system unlimited feeder capacity, but the distinct
disadvantage of requiring a mini mum of 35 8 in. (92 mm) of concrete fill.
This additional slab thickness can frequently be avoided by depressing part
of the slab to accommodate feeder ducts run under the distribution ducts, as
shown in FIGR. 29.

FIGR. 27 Details of a single-level underfloor duct system utilizing three-section
cell duct for both distribution and feeder ducts.

(a) Portion of a typical large open floor space in a commercial facility.
Distribution ducts may be placed as close as on 5-ft (1.5-m) centers to satisfy
dense desk spacing. (b) Three-cell distribution duct utilizes a 4-in. (100-mm)-wide
center cell (4.9 in. 2 [3160 mm^2]) for power and either 3-in. (75-mm)-wide
(3.7 in. 2 [2386 mm^2]) or 6-in. (150-mm)-wide (7.4 in.2 [4773 mm^2]) outer
cells for signal and data cabling. Minimum concrete fill depth is 2½ in. (64
mm), resulting in a minimum 1-in. (25-mm) cover over the distribution ducts.
Service fittings are flush with the floor. (Courtesy of Square D Company.)

FIGR. 28 Typical two-level junction box demonstrates the simplicity of the
two-level system. (Courtesy of Square D Company.) FIGR. 29 Setting a two-level
underfloor duct system. To avoid thickening the fill, a depression in the slab
can accept feeder ducts. Ducts would be run near the bay center to avoid the
negative steel required of joists near columns.

A typical two-level system is illustrated in FIGR. 30. Here, the feeder ducts
run above the distribution ducts and intersect at a specially constructed junction
fitting, into which the distribution ducts partially recess in order to reduce
overall system height. The required concrete fill is either 3 or 4 in. (75
or 100 mm), depending upon the depth of the distribution cells (2 or 3 in.
[50 or 75 mm]).

In all underfloor duct systems, the principal cable capacity bottleneck is
usually the supply point to the feeder ducts. One solution to this problem
uses a special feed arrangement at panels (FIGR. 31). Another possibility is
to subdivide large floor areas, supplying each via a system of multiple feed
points arranged in closets or at wall panels. In such systems, care must be
taken to ensure sufficient inter connection capacity between feed points because
data networks are not only floor-wide but frequently building wide.

Underfloor ducts may be cast into the structural slab in lieu of being installed
in fill or topping, but the slab must be designed to accommodate them. The
use of a fill or topping on the structural slab for an underfloor duct installation
has these advantages:

1. Ducts can be run in any direction, without conflict with structural elements.

1. Additional concrete increases costs directly by increasing the weight of
the structure. This is particularly expensive in seismic designs.

2. The building height may be increased.

In retrofit jobs where underfloor duct is selected rather than one of the
other floor or ceiling race way systems, the ducts will be placed in a new
(added) floor fill.

In conclusion, some general comments on the application of underfloor duct
systems are in order.

Underfloor duct systems are expensive. They can add 50% to the building's
electric system cost, with out consideration of the other construction costs
involved. To justify their use, therefore, a building should meet these criteria:

1. There are open floor areas, with a requirement for outlets at locations
removed from walls and partitions.

2. An under-carpet wiring system is inapplicable.

3. Outlets from ceiling systems are unacceptable.

4. Frequent rearrangement of furniture and other items requiring electrical
and signal service is anticipated.

The facilities that may meet these criteria include many office buildings,
museums, galleries (and other display-case spaces), high-cost merchandising
areas, and selected areas in industrial facilities.

Bear in mind that even in high-cost office construction, underfloor duct systems
are difficult to justify economically unless the spatial/furniture layout will
be likely to change. In doubtful cases, alternate arrangements can be planned
and an intelligent choice made after costs and the impact on the building structure
are studied.

26. CELLULAR METAL FLOOR RACEWAY

The underfloor duct system described previously is best applied to rectilinear
arrangements. More free-flowing arrangements, such as those found in office
landscaping layouts, require a fully accessible floor-if the floor is to be
used for electrification. This may be provided by a cellular (metal) floor
that is an integrated structural/electrical system. The floor can be partially
or completely electrified. One of the many available structural element approaches
is shown in FIGR. 32.

The cellular floor is part of the structural system and is designed accordingly.
Electrical wiring is fed into the cells from header ducts and/or trenches that
run perpendicular to the floor cells and constitute a system of underfloor
ducts in themselves. The header ducts in turn are fed from electric panels
and signal data-transmission and telephone cabinets in much the same manner
as underfloor ducts are fed.

Three types of wiring systems generally run in separate floor cells and header
ducts-electric power, data-transmission wiring, and telephone and signal systems.
The last two may be combined in a single cell only if the signal system voltage
and power level are low and the local telephone company approves. A complete
range of outlets and fit tings is available.

27. PRECAST CELLULAR CONCRETE FLOOR RACEWAYS

This structural concrete system is similar to a cellular metal floor in application
and has the same advantages: large capacity, versatility in that each cell
is a potential raceway, and flexibility in outlet placement and movement. Here
too, as with metal cell constructions, the first cost is higher than that of
standard underfloor duct installation, although the life-cycle cost is frequently
lower, depending upon space use and reconfigurations.

A cell is defined in NEC Article 358 as a "single, enclosed, tubular
space in a floor made of precast cellular concrete slabs, the direction of
the cell being parallel to the direction of the floor member." A feed
for these cells is provided, as with metal cellular floor construction, by
header ducts. Although header ducts are normally installed in concrete fill
above the hollow-core structural slab, a header arrangement with feed from
the ceiling below is also entirely practical. As with a metallic cellular floor,
the cells can be used for air distribution and even for piping, although these
elements are generally installed in a hung ceiling.

FIGR. 31 Due to the large capacity of both distribution ducts and feeder ducts,
central cable feed points such as at electric closets can cause bottlenecks.
Illustrated is one possible solution, consisting of a double-duct feed arrangement.
Signal cable would feed in from cable boxes (not shown). P is a power duct,
T a signal duct. (Diagrams courtesy of Square D Company.)

FIGR. 32 (a) One of many designs for electrified cellular floors. The floor
cells are available in many designs, depending primarily upon the structural
requirements. The trench (illustrated in c) that straddles the cells provides
the electrical feeds through precut holes in the cells.

The trench itself is completely accessible from the top and, when opened,
exposes all the wiring and the cells below. (b) Activated preset insert. Note
that the insert straddles the center (power) cell and provides access to the
two adjoining low-voltage wiring cells. Power and signal wiring are completely
separated at all times by metal barriers. If desired, a standard surface "monument" fitting
can be mounted on the floor, or a connection can be made to under-carpet cables
in lieu of the flush plate shown. When an insert is to be deactivated, the
flush cover plate is simply replaced with a blank plate. (c) Section through
a trench duct, which acts as a feeder for distribution ducts. The trench is
available with or without bottom, in any required height, in widths from 9
to 36 in. (230 to 915 mm), and one, two, or three compartments, depending upon
floor cell design and cabling requirements. (Courtesy of Walker Systems, A
Wiremold Company.)

28. FULL-ACCESS FLOOR

This construction is applicable to spaces with very heavy cabling requirements,
particularly if frequent re-cabling and reconnection are required. It provides
rapid and complete access to an under floor plenum. The system was originally
developed for data-processing areas that require large, fully accessible cable
spaces and large quantities of conditioned air. The solution to both of these
requirements is an infinite-access floor, usually constructed of lightweight
die-cast aluminum panels supported on a network of adjustable steel or aluminum
pedestals. Panels are available from 18 × 18 in. to 36 × 36 in. (457 × 457
mm to 915 × 915 mm), and floor depth is normally 12 to 24 in. (305 to 610 mm),
although taller pedestals are available. The subfloor space thus created can
be used for cabling and also to carry conditioned air either in ducts or by
using the entire space as an air plenum. (In the latter case, the wire and
cable must be suitable for air plenum use; see Fig. 20.) The construction is
usually fireproof. Sufficient floor-to-floor height is necessary to accommodate
the raised floor. This approach to electrical distribution may coordinate quite
well with an underfloor air distribution system (UFAD)-see Section 10.

Where air requirements are limited or non existent and the floor is intended
primarily for cabling, pedestals as short as 6 in. (152 mm) can be used, thus
reducing ceiling height problems (FIGR. 33). In such access floor spaces, use
of multiservice distribution modules and modular wiring avoids cable tangles
and reduces labor costs significantly (FIGRs. 33 to 36).

FIGR. 35 Reinforced nonferrous (aluminum) floors are used frequently in hi-tech
applications requiring the large wiring capacity and convenience of full-access
floors. Floor construction can be stringerless, as illustrated, or with stringers,
as in FIGR. 36b. (Photo courtesy of Tate Access Floors, Inc.)

This system, which is covered in NEC Article 328, was originally developed
as both an inexpensive alternative to an underfloor or cellular floor system
and as a means for providing a flexible floor-level branch circuit wiring system.
Essentially, the system consists of a factory-assembled flat cable (NEC type
FCC), approved for floor installation only under carpet squares, plus the accessories
necessary for connection to 120-V power outlets. The cable itself consists
of three or more flat copper conductors, placed edge to edge and enclosed in
an insulating material (FIGR. 37). The entire assembly is covered with a grounded
metal shield, which, like a metal conduit, provides both physical protection
and a continuous electrical ground path. In addition, a bottom shield is required,
which is usually heavy PVC or metal.

The cable, when properly installed on a hard, flat surface, is approximately
0.03 in. (0.8 mm) high, and thus essentially undetectable when covered with
carpet. Because carpet squares are designed to be readily removable, the entire
system can be repositioned to meet changing furniture layout requirements with
a minimum of disruption and no structural work. The cable is designed to carry
normal physical loads such as office traffic and furniture placement without
affecting its electrical performance.

The attractiveness and simplicity of the system led to the development of
similarly designed flat, low-tension (voltage) cables for signal and communication
wiring (FIGR. 38) and, more recently, both electrical and fiber-optic cables
and accessories for data transmission. Manufacturers also offer a complete
line of junction fittings, connectors, adapters, and receptacles (FIGR. 39).

The problems inherent in this type of on-the floor wiring system, such as
cable crossings, splicing, interfacing with round cable systems, interconnections
at floor boxes and fittings, feed connections from cabinets, underfloor ducts,
floor cells, and through-the-floor fittings, have all been solved by a full
line of manufactured devices designed for specific situations.

Because under-carpet wiring systems are separate and distinct from wire and
conduit systems, they, like underfloor duct systems, are usually shown on a
separate electrical plan. A small plan typical of this type is shown in FIGR.
40. Figures 41 and 42 are photographs of essential portions of such an
installation. Note that a complex system such as that shown in FIGR. 42 requires
recessing a floor box into the slab, which to an extent contradicts the essential
simplicity and flexibility of an under-carpet system. Although these systems,
at least in their simplest form, are particularly applicable to retrofit work,
their low cost, combined with the inherent advantages of a flexible FIGR. 37
Schematic section through one design of NEC type FCC under-carpet cable. The
copper conductors illustrated are the equivalent of No. 12 AWG. The PVC acts
as insulation, and the polyester as both insulation and physical protection.
All designs require a metallic top shield and a metallic or nonmetallic bottom
shield for physical protection.

FIGR. 38 Pre-terminated 25-pair under-carpet telephone cable.

These cables are commercially available in lengths from 5 to 50 ft (1.5 to
15 m) in 5-ft. (1.5-m) increments. (Reprinted with permission of AMP.)

FIGR. 39 Typical components of an under-carpet wiring system. The under-carpet
FCC power cable is shown without the metallic top shield required in actual
installation. It is a color-coded, five-conductor cable (neutral, equipment
ground, and three circuit conductors or two circuit conductors and an isolated
ground conductor). The floor outlets shown are front, single-power outlet;
rear (left to right), duplex power outlet (one of which has isolated ground);
standard duplex power outlet; and combination data cable, communications, and
telephone outlet. (Courtesy of Hubbell, Inc.) floor-level wiring system, particularly
in open office areas, has made them a widely used first choice in new construction
as well.

FIGR. 40 Typical layout of under-carpet power and low-voltage/data cabling
for a small office. A power, phone, and data cable connection on the floor
is provided under or immediately adjacent to each desk . (Reproduced with permission
of AMP.)

FIGR. 41 Under-carpet flat power cables connect to round supply cables in
a flush wall box and then extend to a combination power/low-voltage/data floor
fitting. Data cables are connected to the combination floor fitting from their
system boxes, either individually or via other floor fittings. (Photo courtesy
of Walker Systems, A Wiremold Company.)

30. CEILING RACEWAYS AND MANUFACTURED WIRING SYSTEMS

The need for flexibility in a facility's electrical system coupled with the
high cost of underfloor electrical raceway systems encouraged the development
of equivalent over-the-ceiling systems. These systems are actually more flexible
than their underfloor counterparts because they energize lighting, pro vide
power and telephone facilities, and even supply outlets for the floor above,
in addition to permitting very rapid layout changes at low cost. This last
characteristic is particularly desirable in stores where frequent display changes
necessitate corresponding electrical facility changes. Beyond the extreme flexibility
made possible by the ceiling raceway system, it has the additional advantage
that the system itself, not being cast in concrete like its underfloor counterpart,
can be altered at will. Thus, not only layout changes (as mentioned previously)
but also changes in space function can readily be accommodated. This is a particularly
important characteristic in merchandising and educational facilities, where
space function can be repeatedly changed during the course of a building's
life.

Details vary among manufacturers but the systems are essentially the same
and, in principle, resemble underfloor systems. A typical system is constructed
of metallic or nonmetallic surface type raceways arranged in a tree formation
(i.e., large trunk [header] raceways feed multiple smaller branch [distribution]
raceways, and so on). The raceways are hung in the ceiling plenum from the
concrete slab above. The hung ceiling must consist of lift-out panels because
this type of wiring system is not permitted in spaces rendered inaccessible
by the building structure. Header ducts (large area raceways) are fed from
electrical panels and from signal, data, and telephone cabinets in the electrical
and low-voltage wiring service closets, respectively.

Data headers are normally larger than the power header and can carry other
low-voltage, low-power signal wiring as well. Distribution ducts (laterals)
tap onto the headers. These laterals act as sub-distribution raceways, feeding
lighting fixtures and data, signal, telephone, and power outlets on the same
floor and, via poke-through fittings, outlets on the floor above.

The standard method for extending wiring from the ceiling plenum raceways
to floor-level or desk-level signal and power outlets uses vertical multi-section
raceways fed from the top (see FIGR. 43). These service poles are available
in a large variety of designs, finishes, and cross-sectional raceway areas
and are easily installed in almost any location. They may be prewired and usually
contain several power outlets, a telephone connection, and possibly data cable
outlets. The result in a hung-ceiling office area or an exposed ceiling slab
area (FIGRs. 44 and 45) is certainly less elegant than that of a floor-level
wiring system, but for most users it is satisfactory, and its low cost compared
to any type of floor-duct system is a prime redeeming feature.

When electrical connections to poles, lighting fixtures, receptacles, and
communication/data outlets are made with hard wiring, considerable field labor
is required, with a corresponding high cost. Furthermore, the relative permanence
of such wiring lessens the inherent flexibility of the race way system. To
solve both problems, a number of manufacturers have developed a line of modular
branch-circuit wiring elements. These, covered in NEC Article 604 under the
very logical name manufactured wiring systems, consist of metal-clad or armored
cable sets terminating in polarized plugs.

Ceiling raceways can be equipped with matching receptacles, and connection
to fixtures, poles, and other devices becomes a simple matter of plug insertion.

FIGR. 43 Typical floor-to-ceiling electrical/communication raceway poles.
Units are available in a wide variety of shapes, sizes, and cross-sectional
configurations in aluminum and steel. (Courtesy of Hubbell Premise Wiring.)

FIGR. 44 (a) Poles are fed at the top from the suspended ceiling or from exposed
ceiling raceways. These feeds can be either conventional hard-wired or modular
(plug-in), as shown. Modular connectors are used for power and low-voltage
(telephone, communication, data) wiring. (b) Two of the many cross-sectional
configurations available are illustrated. Other designs divide the pole into
three sections to suit the specific application. (Courtesy of Hubbell Premise
Wiring.)

FIGR. 45 Power poles extend down from the ceiling to any desired height. In
this library, power is required above the base cabinets, and the power pole
is easily arranged to supply it. (Courtesy of Wiremold Company.)

The result is a wiring system of extreme flexibility in which even extensive
changes can be made very rapidly with minimal disruption and virtually no mess.
Manufactured wiring systems are only permitted in accessible areas, for logical
reasons. They are also applicable to access floor spaces, as seen in FIGRs.
33 to 36. The additional cost of manufactured wiring elements is frequently
offset by the labor savings, even upon initial installation and certainly after
one or two field changes. Cable sets are available for power (120 V and 277
V), telephone, and all types of low-voltage signal equipment. The cables must
be approved for use in conditioned-air plenums and suspended ceilings.

To take full advantage of the potential labor cost savings inherent in the
system, field labor must be minimized. This is accomplished by factory-equipping
all utilization equipment, including lighting fixtures, with appropriate plug-in
connectors.

FIGR. 46 Manufactured modular wiring assemblies are used for tap connections
to feed ceiling lighting fixtures or any other ceiling connection, as well
as a complete range of junction, switching, tap, and poke-through units. (Courtesy
of Walker Systems, A Wiremold Company.)